1) Field of the Invention
The present invention relates to a packet transmission device and a packet transmission method that is connected with a plurality of communication lines and that transmits received packets, and more particularly, to a packet transmission device and a packet transmission method that can restart packet communications quickly, even when a failure occurs in a communication line in use.
2) Description of the Related Art
At present, packet communications are carried out by use of plural packet transmission devices. When there are plural transmission routes, packet transmission devices calculate costs of the respective transmission routes and select the most suitable transmission route, and use a communication line corresponding to the selected transmission route and thereby transmit packets to a destination.
Further, current packet transmission devices have various redundancy functions so as to improve reliability of packet communications, in preparation for instances of occurrence of a failure with communication lines and so forth.
For example, in a switch loaded with Uplinkfast function described in “Concept of Uplinkfast”, Cisco Systems, Ltd., [on line], [searched on Sept. 29, 2004]. internet <URL: http://www.cisco.com/japanese/warp/public/3/jp/service/manual_j/sw/ca t60/65scg/chapter09/09_stp_enha.shtml>, when one port corresponding to a redundancy structured communication line, connected with a host switch, is set for forwarding, and the other port is set for blocking, at occurrence of a failure with the port (communication line) for forwarding, the port for blocking is changed for forwarding. Then, from this port that becomes newly for forwarding, a dummy multicast frame (DMF) where MAC addresses of all the terminals under control are send source MAC addresses is sent, and a learning table memorized in a switch (packet transmission device) at host side is corrected.
The learning table is a table where ports and addresses of a communication line are corresponded to one another, and addresses registered (entered) in the learning table and send destination addresses of received packets are compared, thereby a port from which received packets are sent is specified, and packets are sent out from the specified port.
Namely, in the Uplinkfast, a DMF is sent, and addresses corresponded to the port of communication line where a failure has occurred are corrected one by one so as to correspond to the port of normal communication line, thereafter, packet communications are restarted.
However, in such a conventional technology, at occurrence of a failure with a communication line, it is not possible to quickly restart packet communications, which has been a problem with the conventional technology.
At occurrence of a failure with a communication line in use, addresses corresponded to the port of the communication line concerned are corrected one by one, accordingly, packet communications cannot be restarted until a DMF is sent, and all the addresses are corrected so as to correspond to the port of normal communication line.
Further, in many instances, a large number of packets are sent from a port to various destinations, accordingly, at occurrence of a failure with communication line to the port, to correct a large number of addresses corresponded to the port concerned, it is necessary to send the DMF for many times, which has been a further serious problem with the conventional technology.